docs: def p0f(pkt):
      """Passive OS fingerprinting: which OS emitted this TCP packet ?
  p0f(packet) -> accuracy, [list of guesses]
  """
      db, sig = packet2p0f(pkt)
      if db:
          pb = db.get_base()
      else:
          pb = []
      if not pb:
          warning("p0f base empty.")
          return []
      #s = len(pb[0][0])
      r = []
      max = len(sig[4].split(",")) + 5
      for b in pb:
          d = p0f_correl(sig,b)
          if d == max:
              r.append((b[6], b[7], b[1] - pkt[IP].ttl))
      return r